Electric switch of the mercury type



July 7, 1953 E. M CABE ELECTRIC SWITCH OF THE MERCURY TYPE Filed April 14, 1951 INVENTOR. IRA E. M CABE Patented July 7, 1953 UNITED STATES FATENT OFFICE 2,644,870 ELECTRIC SWITCH OF THE MERCURY TYPE Ira E. McCabe, Chicago, Ill.

Application April 14, 1951, Serial No. 221,052

8 Claims.

1 The present invention relates to mercury switches and has reference in particular to double-acting switch structure enclosed in a sealed tube and which when connected to a source of electrical energy will operate in an improved manner to intermittently make and break the electric circuit.

Mercury switches of the general type wherein the switch structure is sealed within a glass tube have certain desirable advantages which make them particularly useful under the varying conditions to which the same may be subjected. Such switches are characterized as being adapted for use over long periods of time, and the sealing of the switch structure results in immunity from oxidation or pitting of the contacts and also effectively excludes dust and dirt and prevents corrosion, all of which would adversely afiect the operation and life of the switch elements. In addition, sealed mercury switches have the further characteristic of being highly suitable for use in high humidity and explosive charged atmospheres where the ordinary type of open solid metal to metal contact would prove faulty or hazardous in operation.

Mercury switches embodying contact members mounted for movement and which are rendered operative through the expansion of an operating part upon the passage of an electric current through the switch are well known to those skilled in this art. One such form as disclosed in my Patent No. 2,564,853, granted August 21, 1951, and entitled Thermally Operated Electric Switch, embodies in combination a resiliently r flexibly mounted contact member which is placed under tension by an expan'sible and contractible wire element to establish a closed circuit. The wire element is included in the switch circuit so that upon the passage of current of a certain value through the wire element expansion of the same takes place to release the tension on the flexibly mounted contact member, with the result that the member has movement to operate the switch contacts. Upon establishing an open circuit the wire element contracts and the flexibly mounted contact member returns to closed circuit position. This intermittent operation continues for the period during which the switch structure is connected to the source of electrical energy.

An object of the present invention is to provide a novel type of mercury switch having doubleacting switch mechanism sealed within the glass container thereof and which mechanism will operate to alternately make and break the electric circuit with precise uniformity of the on and off intervals over a long period of time.

More particularly, the invention in its basic aspect comprehends switch operating mechanism embodying a pair of contact members, both of which are movable by separate operators in a specified manner to control an electric circuit. Although the contact members have separate operators, they must act in unison, neither operator can act without the operation of the other. This conjoint action of the contact members constitutes a decided improvement in mercury switches of the intermittent type since it broadens their applications of use and which is accomplished without increasing the size of the switch structure nor materially adding to the cost of production. I

In the switch structure disclosed in the copending application herein identified and those previously mentioned as well known in the art, currents of appreciable value are required in order to eiiect movement of the switch contacts. This is due to the use of materials which are chosen as to their physical and electrical characteristics for providing long life and ruggedness to the device along with the desired performance. Accordingly, the use or" such materials imposes limitations with respect to the degree of switch contact movement obtainable under varying current conditions. When the switch structures are made sufficiently large to provide the mechanical requirements necessary for satisfactory operation and dependability, currents of larger amperage than desired become a requisite for their operation.

Therefore, another object of the invention isto improve the known type of intermittently operated switches to the extent that they may be made operative in response to currents of small amperage without impairing their structural stability.

Since the nature of the materials selected for the above described known switches lessens the amplitude of movement of the operating parts under low current conditions, it is another object to provide a mercury switch embodying contact members both of which have movement as a result of flow of current through the switch. By moving both contact members suificient separation of the contacts can be obtained although movement of each member is held to a minimum and the operating switch structure need not attain large dimensions in order to produce the desired results. By multiplying the movement in this manner materials can be selected which will not impair the ruggedness of the switch structure and the switch will be just as responsive to small currents so that the net result is to materially increase the useful life of the switch.

With these and various other objects in view, the invention may consist of certain novel features of construction and operation, as will be more fully described and particularly pointed out in the specification, drawing and claims appended hereto.

In the drawing which illustrates two embodiments of the invention and wherein like reference characters are used to designate like parts- Figure l is a view in section of a mercury switch embodying double-acting contacts in accordance with the present invention;

Figure 2 is a View in section of a modified form of switch structure coming within the present invention;

Figure 3 is a top plan view of the switch of Figure 2 showing the location of the four terminals; and

Figure 4 is a detail view of the insulated connecting link for connecting the movable contact members.

Referring now in more detail to the drawings, the embodiment selected for illustrating the present invention as shown in Figure 1 consists of an hermetically sealed container ID of glass or other non-conducting material which is provided at one end with a well I I adapted to serve as a reservoir for a pool of mercury l2 and in which is immersed a capillary tube l3 extending above the surface of the pool of mercury and having an opening I4 whereby as a result of capillary action there is provided a contacting surface or meniscus of mercury above the level of the pool. The capillary tube as herein disclosed generally conforms to that shown and claimed in the McCabe Patent No. 2,325,785, granted August 3, 1943. In the device of this invention the capillary tube is supported for and has movement to the same extent that the contact member has movement, so that the circuit is closed through the switch when the operating switch parts move into contact with each other and the circuit through the switch is broken when the parts separate as a result of movement away from each other.

The end of the glass container opposite the well II is sealed as at [5 and the sealed end supports the terminals 16 and 11. Within the container the electrodes l8 and 2t] are suitably secured as by welding or brazing to the depending ends of the terminals l6 and ll, respectively, and accordingly the electrodes are suitably supported in fixed relation within the tube and electrically connected to the terminals. A bead 2| of glass or similar insulating material is located within the sealed glass container, being supported by the depending ends of the electrodes I8 and 20. At locations spaced outwardly of the electrodes the glass bead positions supporting elements 22 and 23, respectively, which depend some distance below the head. The operating parts of the present switch are supported from the elements 22 and 23 and this structure will now be described in detail.

A contact supporting member 24 comprising a resilient or flexible member is suitably fixed at its upper end to the depending end of supporting element 22. The supporting member 24 at its lower end is suitably fixed to the support 25 attached to, or which may form a part of the capillary tube l3. In order to control movement of the capillary tube an expansible and contractible wire element 26 is provided and 4 which extends between the electrode l8 and the support 25, being fixed at its respective ends to said parts. When the wire element is cold and contracted it serves to tension the flexible member 24, providing a slight bow in the member and accordingly the capillary tube is positioned substantially centrally within the mercury well II.

A similar contact supporting member 21 is supported by element 23, the same also comprising a resilient or flexible member, and which depends within the container in proper spaced relation with 24 and the length of these two members is about the ame. The contact member 28 is suitably secured as by welding to the lower end of 21 and in order to control movement of the contact member an expansible and contractible wire element 29 is provided, the same extending between the electrode 20 and the member 28 and being secured to these parts. When the wire element 28 is cold and contracted it tensions the flexible member 21, forming a slight bow in the member and which has the effect of locating the movable contact member 28 in contact with the meniscus of mercury provided by capillary tube Hi.

It will be clearly apparent from the above description that when no current passes through the switch structure the wire elements 26 and 29 are contracted, which tensions their respective flexible members, namely, 24 and 21, causing a slight bow in each member to thereby position the capillary tube I3 and the contact member 28 so that the contact member is in engagement with the meniscus of mercury provided by the capillary tube. Since the contacts of the switch are closed an electric circuit can be completed through the switch and which is caused to flow through the wire elements 26 and 28, respec tively. The action of the current in flowing through the expansible and contractible wire elements will raise their temperatures, thus causing the same to expand or elongate, with the result that the capillary tube moves in a direction toward the left due to the tension of the v flexible member 24. The elongation of the wire ments will continue until the contacts of the switch separate to break the circuit through the switch. When current ceases to flow through the wire elements 26 and 29 they begin to cool and as they contract they function to move the capillary tube l3 and contact member 28 toward each other. Presently engagement of the contact member 28 with the meniscus of mercury in capillary tube l3 will again take place, whereupon the circuit through the switch is completed and the cycle of operation as herein described is repeated. Intermittent making and breaking of the electric circuit is thereby accomplished, all in accordance with the preceding description.

A material improvement in the snap acting operation of the present switch structure can be secured by providing a contact point on member 28 which is readily wetted by mercury. By the use of a contact point, which includes a portion that wets readily with the mercury it is possible to cause the mercury to adhere to and stretch out as the contact member separates from the capillary tube until a complete break has been effected. There is accordingly provided a quick break in the circuit and which when made creates a ap sufficient to prevent arcing across the contacts.

acting four terminal switch, with one of the additional terminals comprising a fixed electrode in electrical connection with the pool of mercury and the other additional terminal comprising a movable contact member adapted to contact a second meniscus of mercury provided by the capillary tube. As a result, this modified form of the invention provides switch structure capable of making and breaking two electric circuits intermittently and which ,is accomplished alternately so that when one circuit is closed the other circuit is open.

The device of Figure ,2 consists of .an hermetically sealed container I I0 having a mercury containing well III within which is immersed the capillary tube H3. The sealed end of the glass tube, namely, H5, supports a pair of terminals H3 and Ill, which electrically connect with electrodes H8 and I disposed within the glass container and which in turn support the glass Themodification shown in Figure 2 is a doublethat the contact member I28 engages the meniscus of mercury provided by capillary tube II3. When contact member I28 is in closed circuit position the member I34 will be located 'in open circuit position and vice versa due to the manner in whichthese parts are joined by the yoke I31.

When the switch of Figure 2 is interposed in an electric circuit, current will flow through the wire elements I26 and I29 since this circuit of the switch is closed. As the wire elements become heated they tend to expand, producing a separation of contact I28 with the meniscus of mercury provided by the capillary tube H3, it

bead I2I, all in a manner as described in connection with the switch structure of Figure 1. The supporting elements I22 and I23 depend below the non-conducting bead and provide supporting means for the resilient and flexible contact supporting members 124 and I21, respectively. The contractible'and expansible wire elements I25 and I29 tension the flexible members in a manner as previously explained and which have respectively secured to their lower depending ends the capillary tube H3 and the movable contact member I28. 7

It will be apparent from the preceding description that in this modified form of the invention the electric circuit represented by the terminals H6 and H1 is controlled by the same switch structure as disclosed in Figure 1. However, it was previously stated that this form of switch simultaneously controls two electric circuits, the second circuit being represented by the terminals I33 and I3'I. The terminal I3I comprises the fixed electrode I32 disposed within the sealed glass container and which dips into the pool of mercury H2 at its lower end to thereby make an electrical contact with the mercury and which is maintained as long as the pool of mercury is located in well I I I.

The terminal I provides the fixed electrode 33, having location within the container on the side opposite electrode I32. The fixed electrode I33 provides a support for the movable contact member I36 which is joined to the electrode by the resilient and flexible metal strip I35. This I flexible connection of the contact member I34 with its fixed electrode permits movement of the member so that the same may have contact with the meniscus of mercury provided by the opening I36 in the capillary tube.

The movable contact I28 is joined to the movable contact I34 by the yoke I31 shown in detail in Figure 4. The terminal end I38 of the yoke is suitably fixed as by welding to contact member I23 and. in a similar manner the terminal end i313 of the yoke is fixed to the contact member I3. A glass bead I46 or other suitable insulating material is interposed centrally of the yoke in order to insulate the contact members.

When no current flows through the switch of Figure 2, the parts will assume the position as shown, with the wire elements I26 and I29 being contracted to apply tension to their respective flexible members I24 and I21, with the result being understood that both parts of the switch structure will move away from each other dueto the tension applied thereto by the flexible members I24 and I21. As the capillary tube moves away from member I28 it moves toward member I34. Simultaneously therewith memher I34 moves toward the capillary tube. Therefore as one of the circuits represented by terminals H8 and H1 is broken the other circuit of the switch represented by terminals I36 and I3! is closed. This second circuit remains closed until the wire elements I26 and I 29 cool and contract sufficiently to again effect closing of contact I28. This closing movement of contact F28 produces an opening movement of contact 34. In this manner the two circuits controlled by this modified form of switch are intermittently made and'broken and operation takes place alternately as regards the circuits so that when one circuit is closed the other is open.

The invention is not to be limited to or by etails of construction of the particular embodiment thereof illustrated by the drawing, asvarious other forms of the device will of course be apparent to those skilled in the art without departing from the spirit of the invention or the scope of the claims.

What is claimed is:

1. An electric switch comprising a sealed container, a pool of mercury within the container, a capillary tube and movable contact means within the container, flexible means supporting the capillary tube with one end immersed in the mercury pool, said capillary tube presenting a contacting surface of mercury above the pool, other flexible means supporting the movable contact means for contact with said contacting surface of mercury provided by the capillary tube whereby to close an electric circuit, an expansible and contractible wire element for each of the flexible means, each wire element when cold and contracted tensioning its flexible means to position the capillary tube and said contact means to establish a closed circuit position so that the contact means is in engagement with the contacting surface of mercury, and said wire elements being included in the electric switch circuit for controlling movement of the capillary tube and movement of the contact means with respect to each other.

'2. An electric switch comprising a sealed container, a pool of mercury within the container,

a capillary tube and movable contact means with-' in the container, flexible means supporting the capillary tube with one end immersed in the mercury pool, said capillary tube presenting a contacting surface of mercury above the pool, other flexible means supporting the movable contact means for contact with said contacting surface of mercury provided by the capillary tube whereby to close an electric circuit, an expansible and contractible wire element for each of the flexible means, each wire element when cold and contracted tensioning its flexible means to position the capillary tube and said contact means to establish a closed circuit position so that the contact means is in engagement with the contacting surface of mercury, and means electrically connecting the wire elements in series relation in the switch circuit whereby to control movement of the capillary tube and movement of the contact means with respect to each other.

3. An electric switch comprising a sealed container, a pool of mercury within the container, a capillary tube within the container, a flexible supporting member supporting the capillary tube with one end immersed in the mercury pool, said capillary tube presenting a contacting surface of mercury above the pool, movable contact means within the container, a second flexible supporting member supporting the movable contact means to permit make and break contact of the same with said contacting surface of mercury provided by the capillary tube whereby to close an electric circuit, an expansible and contractible wire element for each of the flexible supporting members, each element when cold and contracted tensioning its flexible supporting member to position the capillary tube and the contact means to establish a closed circuit position so that the contact means is in engagement with the contacting surface of mercury, and said wire elements being included in the electric circuit for controlling movement of the capillary tube and movement of the contact means with respect to each other.

4. An electric switch comprising a sealed container, a pool of mercury within the container, a capillary tube within the container, a flexible supporting member supporting the capillary tube with one end immersed in the mercury pool, said capillary tube presenting a contacting surface of mercury above the pool, movable contact means within the container, a second flexible supporting member supporting the movable contact means to permit make and break contact of the same with said contacting surface of mercury provided by the capillary tube whereby to close an electric circuit, an expansible and contractible wire element for each of the flexible supporting members, each element having connection with its flexible supporting member for tensioning the member when the element is cold and contracted to thus position the capillary tube and the contact means to establish a closed circuit relation so that the contact means is caused to engage the contacting surface of mercury, and means in sealed relation with the container also having connection with each element respectively, said means comprising the terminals of the switch whereby the said wire elements are electrically connected in series relation in the switch circuit to thereby control movement of the capillary tube and movement of the contact means with respect to each other.

5. An electric switch comprising a sealed container, a pool of mercury within the container, a pair of movable contact members within the container, the first movable contact member having one end immersed in the mercury and providing capillary means presenting a contacting surface of mercury above the pool, the second movable contact member being adapted to make and break contact with the first member at said contacting surface of mercury to thereby control an electric circuit, a first flexible supporting means fixed at one end of the container and supporting the first movable contact member at its other end, a second flexible supporting means fixed at one end of the container and supporting the second movable contact member at its other end, and expansible and contractible wire element for each of the flexible supporting means, means electrically connecting the wire elements in series relation to the respective terminals of the switch circuit, each said element when cold and contracted tensioning its flexible supporting means to position the pair of contact members in engagement at said contacting surface of mercury to close the switch circuit, and each said element when heated and expanded as a result of current flow through the same permitting movement of the pair of contact members in opposite directions away from each other as a result of the tensioning of the flexible supporting means to thereby break the switch circuit.

6. An electric switch comprising a sealed container, a pool of mercury within the container, a first movable contact within the container having one end immersed in the mercury pool and providing capillary means presenting a contacting surface of mercury above the pool, a flexible supporting member fixed at one end of the container and supporting the first movable contact at its other end, a second movable contact within the container adapted to make and break contact with the said contacting surface provided by the first movable contact whereby to control an electric circuit, a second flexible supporting member fixed at one end of the container and supporting the second movable contact at its other end, an expansible and contractible wire element for each of the flexible supporting members, each wire element when cold and contract ed tensioning its flexible supporting member to position the first and second movable contacts toward each other, whereby contact is effected at said contacting surface to close the switch circuit, and each said wire element when heated and expanded as a result of current flow through the same permitting movement of the first and second movable contacts in opposite directions away from each other as a result of the tensioning of their flexible supporting members to thereby break the switch circuit.

7. An electric switch comprising a sealed container, a pool of mercury within the container, a first movable contact within the container havmg one end immersed in the mercury pool and providing capillary means presenting a portion of said mercury above the pool, a flexible supporting member fixed at one end of the container and supporting the first movable contact at its other end, a second movable contact within the container adapted to make and break contact with said portion of mercury provided by the first movable contact whereby to control an electric circuit, a second flexible supporting member fixed at one end to the container and supporting the second movable contact at its other end, an expansible and contractible wire element for each of the flexible supporting members, each wire element when cold and contracted applying tension to its flexible supporting member to thereby position the members toward each other with the first and second movable contacts in closed circuit relation, each said wire element when heated and expanded as a result of current flow through the same permitting movement of the first and second movable contacts in opposite directions away from each other as a result of the tension of their flexible.

supporting members to thereby break the switch circuit, an independently mounted contact flexibly supported within the container and adapted to have make and break contact with said portion of mercury provided by the first movable contact whereby to control a second electric circuit, and insulated means linking said independent contact with the second movable contact whereby said independent contact is caused to move with said second movable con-= tact into and out of engagement with the said portion of mercury.

8. An electric switch comprising a sealed con-= tainer, a pool of mercury within the container, a capillary tube within the container, a flexible supporting member supporting the capillary tube with one end immersed in the mercury pool, said capillary tube presenting a portion of said mercury above the pool, a movable contact member within the container, a second flexible supportin member supporting the movable contact member to permit make and break contact of the same with said portion of mercury provid ed by the capillary tube whereby to close an electric circuit, an expansib-le and contractible wire element for each of the flexible supporting members, each element when cold and contracted applying tension to its flexible supporting member to position the members toward each other whereby the capillary tube and the contact member are in closed circuit relation with the contact member in engagement with said 7 portion of mercury, each said wire element when heated and expanded as a result of current flow through the same permitting movement of the capillary tube and the contact member in opposite directions away from each other as a result of the tensioning of their flexible supporting members to thereby break contact with the portion of mercury provided by the capillary tube, an independently mounted contact member flexibly supported within the container and adapted to have make and break contact with the portion of mercury provided by the capillary tube, a fixed electrode extending through the sealed end of the container and having contact with the pool of mercury, and insulated means link ing said independently mounted contact member with the movable contact member whereby said independent contact member is caused to move with said movable contact member into and out of contact with said portion of mercury whereby to control a second electric circuit including the said independently mounted contact member and the fixed electrode.

IRA E. MCCABE.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 1,923,509 Rozumek Aug. 22, 1933 2,121,235 Hunciker June 21, 1938 2,299,767 Schmidinger Oct. 27, 1942 2,325,785 McCabe Aug. 3, 1943 

